Opposed Twin Restoration Project

[Walt 2002]

Well cylinder ridge is caused because that is where the rings stop traveling up the cylinder. Measure the ring gap at the top of ring travel and at the bottom of ring travel. Rings do not travel to bottom of bore, only the piston skirt does. I almost always use .010" oversize rings hand fitting to .008" ring gap at bottom of ring travel. I do that, I do not recommend nor encourage anyone else to do it. Valve guides should be no problem for a Service Tech, easy and cheap to install, shop should have reamer, driver and finish ream.

Never saw a camshaft look like that and I have rebuilt a bunch of these engines. You may want to look at the cams in other engines you say are in shop junk. Check valve seats for tightness, especially the exhaust valve seats.

If there is no coil on engine now to look at, when you install coil, make sure it is right side up. Some are marked, others not. Install with wires heading towards back of engine then they double back under coil and out carb side of engine - common mistake. Also, make sure fuel pump hoses are connected properly, another common mistake. I see you have been pointed to a Service Manual which will be valuable. This engine should be economical to rebuild for your purpose, not figures advanced above.

Walt Conner

 

[Walt 2002]

Follow up, Yes, notch in piston towards flywheel. Important, I see you removed the rods from pistons, check manual for oil hole orientation to camshaft. You mentioned washers with the oil seals, I didn't see that but likely spacers for adjusting end play IF needed.
Walt Conner

 

[Born2Mow]

Well cylinder ridge is caused because that is where the rings stop traveling up the cylinder. Measure the ring gap at the top of ring travel and at the bottom of ring travel. Rings do not travel to bottom of bore, only the piston skirt does.

Walt -
With all due respect, sir, this a correct but incomplete observation. There is no "cylinder ridge" at the lower end of ring travel... it's only at the top of the bore. And it's formed there because that's were combustion chamber pressure is Maximum.

So it's the force of the fuel combustion pushing the rings outward with tremendous force that causes the extreme wear (and thus the "cylinder ridge") at the top of the bore. It's not simply the presence of the rings, but presence of the rings PLUS immense combustion pressure.

 

[bertsmobile1]

There are 2 things that get called ridges
One of them is a carbon build up from oil trapped between the upper ring & the top of the cylinder burning
The other is a groove , just below this which is the maximum ring travel.
You do get an end of wear step at the bottom of the bore but it is nowhere as pronounced as that at the top
Run an inside micrometer down the bore and you will find a tapper from the top to the end of ring travel at the bottom then a step anything from 0,002" to 0,0005"before the unworn section right at the bottom.

 

[TylerFrankel1]

For a first-time engine builder, the most important thing to keep in mind is that you are NOT building a Formula 1 engine. So what if the guides are a little loose ? OK it may burn a cup of oil between changes. Big deal; oil is VERY cheap. Compare the price of the oil burned versus the price of machine work and new parts to make it perfect. One year from now you'll feel really stupid having spent $800 on a complete valve job.... and then having only used the engine for 3 hours.

Typically this is a big pit-fall for guys, especially guys on an internet forum. There are no shortage of "cheerleaders" encouraging you to spend (yours, not theirs) $2000 restoring a machine that has a CraigsList value of $200.

Just my 2 cents.

Thanks for the advice! I took it. I went ahead and ordered the parts I needed and didn't worry about the valves. I got new rings, head gaskets, sump gaskets, PTO seals, etc etc. Finished cleaning block/parts... and rebuilt the motor. Found out my starter motor was too weak... bought a new aftermarket starter (and ignition coil). Cleaned carburetor thoroughly and put in a new pump diaphragm.

She fires right up and runs well after tuning. Needle/seat leaks but since it's a fuel pump, not gravity feed, it's not bad, and I'll put a shut-off inline instead of repairing it because I'm cheap. Now I'm working on piecing together the cooling shrouds that were missing from eBay listings. Having trouble finding a reasonably priced 691197 air shroud for the lower cylinder head. Once I do I'll get the rest put together and it should be about complete. I'm using 10W-30 synthetic at the moment but am considering changing it... I've run it a total of ~4 minutes across several starts (don't want to run long without cooling shrouds) and I realized that synthetic might be a bad idea for breaking in the rings. Anyway, here's a video of it running:

(Warning - it's loud - I still need to create an exhaust for it (another reason I don't run it for more than a minute at a time)

 

[TylerFrankel1]

In regards to the other posts I've seen here, whatever ridges there may have been are not noticeably present anymore after honing. This motor was internally in pretty good shape, and I have no idea what that cam looked like that for. I think the brown was the result of some weird additive or oil used by the previous owner causing buildup on all the surfaces that were not wear surfaces, (and the non-lobe part of the cam doesn't really wear). That brown discoloration was on most all the parts... but like I said, it runs good.

I work at a reputable shop and we don't have valve reamers anymore. Unfortunately, the parts and labor cost for total engine rebuilds doesn't make economical sense for most customers anymore. If you were to really go through a full rebuild and replace valve guides, bore/hone cylinders, check the crank/piston pins with micrometers, replace rings, grind valves, etc. you'd be looking at well over 5 hours of labor plus parts... which costs more than a new engine or good used engine in most cases. Re-sealing a motor or replacing a crank is usually the most in depth a repair gets before motor replacement. I thought about this repair before committing to it and remembered what YouTuber Taryl Fixes All always says, "It ain't the space shuttle, it's a lawnmower." If my cylinders are slightly out of round or slightly conical, I'll burn a tiny bit of oil and since I'm a mechanic I check that all the time anyway. It'll run good enough. If I was rebuilding a 454 I might feel differently, but these motors are cheap and parts are too. Taking the motor on/off takes 20 minutes. And as of right now it's running great and doesn't smoke (Except briefly at startup because of that leaky needle & seat I mentioned).

Thanks for y'alls thoughts and feedback.